Method, apparatus and system for tracking an object in a sequence of images

Abstract

A method of tracking an object (e.g., 1110 ) in a sequence of images of a scene, is disclosed. At least one foreground area in the scene is associated with the object ( 1110 ). An event that is affecting the foreground area of the scene is determined A track representation is added to a track corresponding to the object ( 1110 ). The added track representation models the determined event and has a property based on the foreground area. Properties of one or more further track representations of are track updated, based on the foreground area, in order to track the object ( 1110 ).

The claims defining the invention are as follows: 
     
         1 . A method of tracking an object in a sequence of images of a scene, said method comprising:
 determining an event that is affecting a foreground area corresponding to the object, the object being associated with a track having a first track representation;   adding a second track representation to the track, said second track representation being created based on the foreground area prior to the event;   updating the first track representation based on the foreground area while the second track representation is kept; and   matching at least one of the foreground areas with at least one of the first and second track representations to track the object.   
     
     
         2 . A method according to  claim 1 , further comprising deleting one or more of the track representations of the track if the modelled event is false. 
     
     
         3 . A method according to  claim 1 , further comprising deleting one or more of the track representations of the track if the event has ended. 
     
     
         4 . A method according to  claim 1 , wherein the first track representation is an unoccluded track representation. 
     
     
         5 . A method according to  claim 4 , wherein the second track representation is added as an occluded track representation to the track, if a background object is occluding said object. 
     
     
         6 . A method according to  claim 1 , wherein at least one of width, height and location of the area of first track representation is updated while the width and height of the second track representation is kept. 
     
     
         7 . A method according to  claim 1 , further comprising:
 determining a first difference between a determined location of one edge of a track associated with the object and a previously determined location of the corresponding edge of the track,   determining a second difference between the determined location of a further edge of the track and a previously determined location of the corresponding further edge of the track; and   detecting occlusion of the object as the event if the first difference is less than a threshold and the second difference is greater than a threshold.   
     
     
         8 . A method according to  claim 1 , further comprising:
 determining a first difference between an edge of a prediction of a track corresponding to the object and the corresponding edge of a foreground area of the scene associated with the track;   determining a second difference between a further edge of the prediction of the track corresponding to the object and the corresponding further edge of the foreground area of the scene associated with the track; and   detecting an occlusion of the object as the event if the first difference is less than a first threshold and the second difference is greater than a second threshold.   
     
     
         9 . An apparatus for tracking an object in a sequence of images of a scene, said apparatus comprising:
 means for determining an event that is affecting the foreground area corresponding to the object, the object being associated with a track having a first track representation;   means for adding a second track representation to the track, said second track representation being created based on the foreground area of the object prior to the event; and   means for updating the first track representation, based on the foreground area of the object while the second track representation is kept; and   means for matching at least one of the foreground areas with at least one of the first and second track representations to track the object.   
     
     
         10 . A non-transitory computer readable medium having a computer program stored there for tracking an object in a sequence of images of a scene, said program comprising:
 code for determining an event that is affecting a foreground area corresponding to the object, the object being associated with a track having a first track representation;   code for adding a second track representation to the track, said second track representation being created based on the foreground area prior to the event;   code for updating the first track representation based on the foreground area while the second track representation is kept; and   code for matching at least one of the foreground areas with at least one of the first and second track representations to track the object.   
     
     
         11 . A method of detecting occlusion of an object within a captured image of a scene, said method comprising:
 determining a first difference between an edge of a prediction of a track corresponding to the object and the corresponding edge of a foreground area of the scene associated with the track;   determining a second difference between a further edge of the prediction of the track corresponding to the object and the corresponding further edge of the foreground area of the scene associated with the track; and   detecting an occlusion of the object if the first difference is less than a first threshold and the second difference is greater than a second threshold.   
     
     
         12 . An apparatus for detecting occlusion of an object within a captured image of a scene, said apparatus comprising:
 means for determining a first difference between an edge of a prediction of a track corresponding to the object and the corresponding edge of a foreground area of the scene associated with the track;   means for determining a second difference between a further edge of the prediction of the track corresponding to the object and the corresponding further edge of the foreground area of the scene associated with the track; and   means for detecting an occlusion of the object if the first difference is less than a first threshold and the second difference is greater than a second threshold.   
     
     
         13 . A non-transitory computer readable medium having a computer program stored thereon for detecting occlusion of an object within a captured image of a scene, said program comprising:
 code for determining a first difference between an edge of a prediction of a track corresponding to the object and the corresponding edge of a foreground area of the scene associated with the track;   code for determining a second difference between a further edge of the prediction of the track corresponding to the object and the corresponding further edge of the foreground area of the scene associated with the track; and   code for detecting an occlusion of the object if the first difference is less than a first threshold and the second difference is greater than a second threshold.